Combined Heat and Power Technology for Natural Gas Liquefaction Plants

ABSTRACT

Systems and methods for the generation of liquid natural gas (“LNG”) are provided.

CROSS-REFERENCE TO RELATED APPLICATION

Not Applicable

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

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THE NAMES OF THE PARTIES TO A JOINT RESEARCH AGREEMENT

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INCORPORATION-BY-REFERENCE OF MATERIAL SUBMITTED ON A COMPACT DISC

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BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates generally to systems and methods for the generation of liquefied natural gas (“LNG”).

2. Description of the Related Art

Natural gas can be converted to liquefied natural gas (“LNG”) by cooling it to about −161° C., depending on the exact composition of the natural gas, which reduces its volume to about 1/600th of its original value. This reduction in volume can make transportation more economical. For example, the LNG can be transferred to a cryogenic storage tank located on an ocean-going ship. Once the ship arrives at its destination, the LNG can be offloaded to a regasification facility, in which it is converted back into gas by heating it. Once the LNG has been regasified, the natural gas can be transported by pipeline or other means to a location where the natural gas can be used as a fuel or a raw material for manufacturing other chemicals.

The conventional process for LNG production involves gas turbine driven refrigeration compressors. The exhaust flue gas from the gas turbines is typically discharged to the atmosphere. Additional compression power is typically supplied through use of gas turbine generators or other external sources, with the help of large synchronous motors with load commutated inverter (“LCI”) drives, which require additional fuel gas consumption leading to higher operating costs and higher plant greenhouse gas emissions. Synchronous motors are larger, more expensive, less reliable and require more control equipment than induction motors, but large induction motors that can operate at high speeds are not known in the art.

What is needed therefore are systems and methods to reduce fuel gas consumption and greenhouse gas emissions in LNG facilities.

SUMMARY OF THE INVENTION

The present disclosure overcomes one or more of the deficiencies of the prior art by providing systems and methods to recover and utilize waste heat generated in LNG facilities, thereby reducing fuel gas consumption and reducing greenhouse gas emissions. In the present disclosure power to supply all of the LNG plant's electrical demand can be extracted from gas turbine waste heat. The power can be generated in a dedicated onsite power unit that is located to optimize the layout of the overall production facility. The separation of the power facility from the liquefaction area allows for more efficient operation of the power unit and utilization of plot space as the equipment used requires significant space that is not generally available in the liquefaction area.

Another feature of the present disclosure is that the steam produced from waste heat can also be utilized for process heating, thus further reducing the demand for fuel. Heating steam may be taken directly from the steam generators for operations that require higher heating temperatures. For lower temperature heating requirements steam may be extracted at lower pressures from the steam turbine, allowing high value mechanical power to be extracted from the steam to generate electrical power before the steam is supplied to the process heating operations. The low pressure steam extracted from the turbine has the further benefit of reducing the load on the air cooled steam condensers.

An additional and optional feature of the present disclosure is that hydrocarbon waste liquid streams may be burned in the gas turbine exhaust duct to provide supplemental energy needs of the process and to simultaneously eliminate a stream that is otherwise difficult to dispose of economically. Natural gas or other supplemental gas fuel may also be burned if additional energy is required for power production and/or heating services. For flexibility, sparing, and to facilitate plant startups, a separate standalone boiler may also be provided.

The present disclosure provides a system for the generation of liquefied natural gas comprising a first gas turbine, a first steam generator in gaseous communication with the first gas turbine, a second gas turbine, a second steam generator in gaseous communication with the second gas turbine, a steam turbine in gaseous communication with the first steam generator and the second steam generator, and an electrical generator in mechanical communication with the steam turbine. Gas turbines are routinely used in the production of liquefied natural gas, and the present disclosure provides an improved system and process for the production of liquefied natural gas using gas turbines, the improvement comprising a waste heat recovery system comprising a first steam generator in gaseous communication with a first gas turbine, a second steam generator in gaseous communication with a second gas turbine, a steam turbine in gaseous communication with the first steam generator and the second steam generator, and an electrical generator in mechanical communication with the steam turbine. Thus the present disclosure provides for the utilization of the heat generated by the gas turbines used in the production of liquefied natural gas, which previously was wasted, to produce electricity. In certain embodiments enough electricity is produced from the heat generated by the gas turbines to power the entire natural gas production facility.

In additional embodiments the system further comprises a first helper motor and a second helper motor electrically connected to the electrical generator. In further embodiments the first helper motor is mechanically connected to the first gas turbine and the second helper motor is mechanically connected to the second gas turbine. In general the first helper motor and the second helper motor are synchronous or induction motors, although other types of motors can find uses in certain embodiments. The synchronous or induction motors can be connected to voltage source inverter drives, although other types of drives can be connected to the motors in particular embodiments.

The disclosed system can further comprise a first drive shaft attached to the first gas turbine and a second drive shaft attached to the second gas turbine. The disclosed system can further comprise at least a first refrigeration compressor connected or attached to the first drive shaft and at least a second refrigeration compressor connected or attached to the second shaft. In additional embodiments the disclosed system comprises at least a third refrigeration compressor connected or attached to the first drive shaft. In certain embodiments the system further comprises at least a first cooler or a plurality of coolers in liquid communication with the at least a first refrigeration compressor and at least a second cooler or a plurality of coolers in liquid communication with the at least a second refrigeration compressor. The system can further comprise a scrub column in gaseous communication with the coolers. Furthermore, the system can comprise a cryogenic heat exchanger in gaseous communication with the scrub column. As the natural gas has been liquefied at this point in the process, the system can also include a liquefied natural gas storage tank in liquid communication with the cryogenic heat exchanger.

A certain portion of the stored liquefied natural gas will boil off. Therefore, in certain embodiments the system further comprises a boil off gas compressor in gaseous communication with the liquefied natural gas storage tank. In other embodiments the system can comprise a boil off gas compressor motor connected to the boil off gas compressor and electrically connected to the generator. The boil off gas compressor motor is generally a high speed synchronous or induction motor, although other types of motors can find utility in certain aspects of the disclosure. The high speed synchronous or induction motor can be connected to a variable frequency drive, although other types of drives can be used in certain applications.

The present disclosure also provides a waste heat recovery system, comprising a first gas turbine, a first steam generator in gaseous communication with the first gas turbine, a second gas turbine, a second steam generator in gaseous communication with the second gas turbine, a steam turbine in gaseous communication with the first steam generator and the second steam generator, and an electrical generator in mechanical communication with the steam turbine.

The present disclosure additionally provides a method for the reduction of fuel gas consumption during the production of liquefied natural gas in a liquefied natural gas facility comprising a first gas turbine that generates a first amount of waste heat upon operation and a second gas turbine that generates a second amount of waste heat upon operation, comprising utilizing the first amount of waste heat from the first gas turbine in a first heat recovery steam generator to produce a first amount of steam, utilizing the second amount of waste heat from the second gas turbine in a second heat recovery steam generator to produce a second amount of steam, utilizing at least a portion of the first amount of steam and the second amount of steam in a steam turbine, producing electricity from a generator connected to the steam turbine, and utilizing the electricity to power at least a first process that consumes electrical power generated from fuel gas used during the production of liquefied natural gas in a liquefied natural gas facility, thereby reducing fuel gas consumption. The at least a first process that consumes electrical power generated from fuel gas includes, but is not limited to, operation of a first helper motor, operation of a second helper motor, operation of a boil off gas compressor motor or production of electricity used in the liquefied natural gas facility.

The present disclosure further provides a method for the reduction of greenhouse gas emissions during the production of liquefied natural gas in a liquefied natural gas facility comprising a first gas turbine that generates a first amount of waste heat upon operation and a second gas turbine that generates a second amount of waste heat upon operation, comprising utilizing the first amount of waste heat from the first gas turbine in a first heat recovery steam generator to produce a first amount of steam, utilizing the second amount of waste heat from the second gas turbine in a second heat recovery steam generator to produce a second amount of steam, utilizing at least a portion of the first amount of steam and the second amount of steam in a steam turbine, producing electricity from a generator connected to the steam turbine, and utilizing the electricity to power at least a first process that generates greenhouse gas emissions used during the production of liquefied natural gas in a liquefied natural gas facility, thereby reducing greenhouse gas emissions.

Additionally, the present disclosure provides a plant for the generation of liquefied natural gas comprising, an inlet gas reception unit connected to a natural gas pipeline, a gas treating and dehydration unit in gaseous communication with the inlet gas reception unit, a liquefaction unit in gaseous communication with the gas treating and dehydration unit, a storage and loading unit in liquid communication with the liquefaction unit, and a waste heat recovery system in communication with the liquefaction unit, comprising a first steam generator, a second steam generator, a steam turbine in gaseous communication with the first steam generator and the second steam generator, and an electrical generator connected to the steam turbine.

The present disclosure also provides a plant for the generation of liquefied natural gas comprising a pig receiver connected to a natural gas pipeline, a filter coalescer in gaseous communication with the pig receiver, a meter in gaseous communication with the filter coalesce, an acid gas absorber in gaseous communication with the meter, a drier precooler in gaseous communication with the acid gas absorber, a drier inlet separator in gaseous communication with the drier precooler, a plurality of gas driers in gaseous communication with the drier inlet separator, a first gas turbine in gaseous communication with the plurality of gas driers, a first plurality of refrigeration compressors connected to the first gas turbine, a second gas turbine in gaseous communication with the plurality of gas driers, a second plurality of refrigeration compressors connected to the second gas turbine, a mercury adsorber in gaseous communication with the plurality of gas driers, a filter in gaseous communication with the mercury adsorber, a plurality of coolers in gaseous communication with the filter, a scrub column in gaseous communication with the plurality of coolers, a cryogenic heat exchanger in gaseous communication with the scrub column, a LNG storage tank in fluid communication with the cryogenic heat exchanger, a boil off gas compressor in gaseous communication with the LNG storage tank, a high speed motor connected to the boil off gas compressor, a variable frequency drive connected to the high speed motor, and a waste heat recovery system, comprising a first steam generator in gaseous communication with the first gas turbine, a second steam generator in gaseous communication with the second gas turbine, a steam turbine in gaseous communication with the first steam generator and the second steam generator, and an electrical generator connected to the steam turbine.

BRIEF DESCRIPTION OF THE DRAWINGS

The following drawings form part of the present specification and are included to further demonstrate certain aspects of the present invention. The invention may be better understood by reference to one or more of these drawings in combination with the detailed description of specific embodiments presented herein.

FIG. 1. Schematic of a waste heat recovery system.

FIG. 2. Schematic of LNG facility.

DETAILED DESCRIPTION

FIG. 1 is a schematic drawing of a LNG facility waste heat recovery system 100 in accordance with one embodiment of the present invention. Waste heat recovery system 100 comprises a first gas turbine 101 connected to a first plurality of refrigeration compressors 111, although in other embodiments (not shown) the first gas turbine 101 can be connected to a single refrigeration compressor 111. In general refrigeration compressors 111 are rotary type, either centrifugal or axial, although other types and configurations can find utility in further aspects of the present disclosure. The first gas turbine 101 produces hot exhaust gas that travels through a first exhaust line 102 to a first heat recovery steam generator (“HRSG”) 103, which takes boiler feed water from first water line 104 and produces steam that travels through first steam line 105. The HRSG 103 may be installed vertically or horizontally, and may produce steam at one or more pressure levels. The heat recovery device could also use heating fluids other than steam, such as organic fluids (not shown). First exhaust line 102 generally comprises a duct burner (not shown), which can use waste liquid or gas from line 130 and/or supplemental fuel gas from line 132 to produce additional heat for the HRSG 103. Waste heat recovery system 100 also comprises a second gas turbine 112 connected to a refrigeration compressor 118, although in other embodiments (not shown) the second gas turbine 112 can be connected to a plurality of refrigeration compressors 118. The refrigeration compressors 111 and 118 take low pressure refrigerant streams 138, 139, and 141 and compress them into high pressure refrigerant streams 137, 140, and 142. The second gas turbine 112 produces hot exhaust gas that travels through second exhaust line 113 (which can also comprise a duct burner, not shown) to a second heat recovery steam generator 114, which takes boiler feed water from second water line 115 and produces steam that travels through second steam line 116. Second steam line 116 joins first steam line 105 to form third steam line 121, which splits into fourth steam line 122 and fifth steam line 123. Fourth steam line 122 directs steam to higher temperature process heating tasks 106, for example heating of the gas used to regenerate natural gas feed dehydrators. Low pressure steam is extracted from the steam turbine into low pressure steam line 128 and supplies heat to the lower temperature process heating tasks 129, which can include, but are not limited to, natural gas feed heating, and other lower temperature heating demands. Condensate from the process heating tasks 106 and 129 travels through first condensate line 124. Fifth steam line 123 directs steam to steam turbine 107, and wet steam from the steam turbine 107 travels through second condensate line 125 to condenser 143. Condensate from condenser 143 flows through line 144, which joins first condensate line 124 to form fourth condensate line 126, which takes the condensate to a water treatment facility 127. The water is treated to remove dissolved solids and de-aerated to remove oxygen and carbon dioxide. Dissolved solids are also prevented from building up in the water by blowing down a small portion of the water. The blowdown is replaced by makeup water, which is also treated for solids removal and de-aerated. Steam turbine 107 is connected to synchronous generator 108, which generates electricity for a number of different uses in the LNG facility. Electricity passes through power line 109 to power helper motor 110 and helper motor 117, which can each be large induction motors, for example a 25 MW induction motor with voltage source inverter drive that runs at high speeds (e.g., 3600 RPM), provide utility power 119 and power for the buildings and lighting 120, as well as through power line 1011 to power the synchronous or induction electric motor (not shown in FIG. 1; see FIG. 2) that powers the boil-off gas compressor (not shown in FIG. 1; see FIG. 2). Induction motors are more robust (fewer parts which decreases failure rate), up to 30% less expensive, more reliable, smaller and require less control equipment than standard synchronous motors with a load commutated inverter drive, although synchronous motors can be used in certain embodiments. Although not shown in FIG. 1, the steam from the first and second heat recovery steam generators can be directed to a plurality of steam turbines. Fuel for gas turbines 101 and 112 is boil-off gas from line 136. Also shown in FIG. 1 is a conventional start-up boiler 133, which uses fuel gas from line 134 to heat water from water line 135 to produce steam. The steam travels through line 145 and 105 to the steam generator 107, to produce electricity needed for start-up operations.

FIG. 2 is a schematic drawing of a LNG facility 1000 comprising the waste heat recovery system (not shown in FIG. 2; see FIG. 1). A natural gas enters LNG facility 1000 from pipeline 1001 and passes through inlet gas reception 1012, which can include, but is not limited to, such components as a meter (not shown) and a filter coalesce (not shown), through line 1002 to gas treating and dehydration 1013. In addition to dehydration, gas treating can include, but is not limited to, such components as an acid gas absorber (not shown; can be packed or trayed) and a mercury adsorber (not shown; generally sulfur impregnated carbon that reacts chemically with the mercury). Line 1003 conveys treated and dehydrated gas to liquefaction unit 1014, and LNG exits through line 1004 to storage and loading unit 1015, from which LNG is loaded for shipping through line 1005. Liquefaction unit 1014 contains the refrigeration compressors 111 and 118 (shown in FIG. 1), with low pressure refrigerant streams 138, 139, and 141 being compressed by compressors 111 and 118 (see FIG. 1) into high pressure refrigerant streams 137, 140, and 142. High pressure refrigerant streams 137, 140 and 142 feed into evaporators (not shown), which can include propane, propylene, Freon®, ammonia, or a mixed refrigerant, in the liquefaction unit 1014 generating low pressure refrigerant streams that feed back into the refrigeration compressors 111 and 118 (see FIG. 1). The liquefaction unit 1014 can also comprise a scrub column (not shown) and/or a cryogenic heat exchanger (“CHE”, not shown; but typically a spiral wound exchanger or series of such exchangers). The liquefaction unit 1014 could also be a series of brazed aluminum exchangers and separators located inside a cryogenically insulated cold box (not shown). Although not shown, reflux for a scrub column to remove heavy components that could freeze and plug equipment at cryogenic temperatures can be provided by a partial condensing coil inside the CHE. Liquefaction unit 1014 can also comprise a liquid expander (not shown), that removes energy from the LNG, which improves the overall efficiency while driving a generator (not shown) to produce additional electricity. A portion of the stored LNG boils off, and the boil-off gas from storage unit 1015 travels through line 1006 to a boil-off gas compressor 1007, which is powered by high speed synchronous or induction electric motor 1008 using electricity from power line 1011 (see also FIG. 1). The speed of the boil-off gas compressor motor is adjusted by a variable speed drive (not shown) to match the flow and pressure requirements of boil-off gas users. Boil-off gas is routed through line 1009 and split into lines 1010 and 131. Line 1010 flows to gas treating and dehydration 1013 where it is used for regenerating the gas dehydrators, and then flows out through line 136 to be used as fuel in gas turbines 101 and 112. Line 131 conveys boil-off gas not used for fuel back to liquefaction unit 1014 to be re-liquefied.

While the present invention has been shown and described in various embodiments, those skilled in the art will appreciate from the drawings and the foregoing discussion that various changes, modifications, and variations may be made without departing from the spirit and scope of the invention as set forth in the claims. Hence the embodiments shown and described in the drawings and the above discussion are merely illustrative and do not limit the scope of the invention as defined in the claims herein. The embodiments and specific forms, materials, and the like are merely illustrative and do not limit the scope of the invention or the claims herein. 

We claim:
 1. A system for the generation of liquefied natural gas comprising: a) a first gas turbine; b) a first steam generator in gaseous communication with the first gas turbine; c) a second gas turbine; d) a second steam generator in gaseous communication with the second gas turbine; e) a steam turbine in gaseous communication with the first steam generator and the second steam generator; and f) an electrical generator in mechanical communication with the steam turbine.
 2. The system of claim 1, further comprising a first helper motor and a second helper motor electrically connected to the generator.
 3. The system of claim 2, wherein the first helper motor is mechanically connected to the first gas turbine and the second helper motor is mechanically connected to the second gas turbine.
 4. The system of claim 2, wherein the first helper motor and the second helper motor are synchronous or induction motors.
 5. The system of claim 4, wherein the synchronous or induction motors are connected to voltage source inverter drives.
 6. The system of claim 1, further comprising a first shaft attached to the first gas turbine and a second shaft attached to the second gas turbine.
 7. The system of claim 6, further comprising at least a first refrigeration compressor attached to the first shaft and at least a second refrigeration compressor attached to the second shaft.
 8. The system of claim 7, further comprising at least a first cooler in liquid communication with the at least a first refrigeration compressor and at least a second cooler in liquid communication with the at least a second refrigeration compressor.
 9. The system of claim 8, further comprising a scrub column in gaseous communication with the plurality of coolers.
 10. The system of claim 9, further comprising a cryogenic heat exchanger in gaseous communication with the scrub column.
 11. The system of claim 10, further comprising a liquefied natural gas storage tank in liquid communication with the cryogenic heat exchanger.
 12. The system of claim 11, further comprising a boil off gas compressor in gaseous communication with the liquefied natural gas storage tank.
 13. The system of claim 12, further comprising a boil off gas compressor motor connected to the boil off gas compressor and electrically connected to the generator.
 14. The system of claim 13, wherein the boil off gas compressor motor is a high speed synchronous or induction motor.
 15. The system of claim 14, wherein the high speed motor is connected to a variable frequency drive.
 16. A waste heat recovery system, comprising: a) a first gas turbine; b) a first steam generator in gaseous communication with the first gas turbine; c) a second gas turbine; d) a second steam generator in gaseous communication with the second gas turbine; e) a steam turbine in gaseous communication with the first steam generator and the second steam generator; and f) an electrical generator in mechanical communication with the steam turbine.
 17. A method for the reduction of fuel gas consumption during the production of liquefied natural gas in a liquefied natural gas facility comprising a first gas turbine that generates a first amount of waste heat upon operation and a second gas turbine that generates a second amount of waste heat upon operation, comprising: a) utilizing the first amount of waste heat from the first gas turbine in a first heat recovery steam generator to produce a first amount of steam; b) utilizing the second amount of waste heat from the second gas turbine in a second heat recovery steam generator to produce a second amount of steam; c) utilizing at least a portion of the first amount of steam and the second amount of steam in a steam turbine; d) producing electricity from a generator connected to the steam turbine; and e) utilizing the electricity to power at least a first process that consumes electrical power generated from fuel gas used during the production of liquefied natural gas in a liquefied natural gas facility, thereby reducing fuel gas consumption.
 18. The method of claim 17, wherein the at least a first process that consumes electrical power generated from fuel gas is operation of a first helper motor.
 19. The method of claim 17, wherein the at least a first process that consumes electrical power generated from fuel gas is operation of a boil off gas compressor motor.
 20. The method of claim 17, wherein the at least a first process that consumes fuel gas is production of electricity used in the liquefied natural gas facility.
 21. The method of claim 17, comprising utilizing the electricity to power at least a first and at least a second process that consume fuel gas used during the production of liquefied natural gas in a liquefied natural gas facility.
 22. The method of claim 21, wherein the at least a first process that consumes fuel gas is operation of a first helper motor and the at least a second process that consumes fuel gas is operation of a second helper motor.
 23. A method for the reduction of greenhouse gas emissions during the production of liquefied natural gas in a liquefied natural gas facility comprising a first gas turbine that generates a first amount of waste heat upon operation and a second gas turbine that generates a second amount of waste heat upon operation, comprising: a) utilizing the first amount of waste heat from the first gas turbine in a first heat recovery steam generator to produce a first amount of steam; b) utilizing the second amount of waste heat from the second gas turbine in a second heat recovery steam generator to produce a second amount of steam; c) utilizing at least a portion of the first amount of steam and the second amount of steam in a steam turbine; d) producing electricity from a generator connected to the steam turbine; and e) utilizing the electricity to power at least a first process that generates greenhouse gas emissions used during the production of liquefied natural gas in a liquefied natural gas facility, thereby reducing greenhouse gas emissions.
 24. A plant for the generation of liquefied natural gas comprising: a) an inlet gas reception unit connected to a natural gas pipeline; b) a gas treating and dehydration unit in gaseous communication with the inlet gas reception unit; c) a liquefaction unit in gaseous communication with the gas treating and dehydration unit; d) a storage and loading unit in liquid communication with the liquefaction unit; and e) a waste heat recovery system in communication with the liquefaction unit, comprising: i) a first steam generator; ii) a second steam generator; iii) a steam turbine in gaseous communication with the first steam generator and the second steam generator; and iv) an electrical generator connected to the steam turbine.
 25. A plant for the generation of liquefied natural gas comprising: a) a pig receiver connected to a natural gas pipeline; b) a filter coalescer in gaseous communication with the pig receiver; c) a meter in gaseous communication with the filter coalescer; d) an acid gas absorber in gaseous communication with the meter; e) a drier precooler in gaseous communication with the acid gas absorber; f) a drier inlet separator in gaseous communication with the drier precooler; g) a plurality of gas driers in gaseous communication with the drier inlet separator; h) a first gas turbine in gaseous communication with the plurality of gas driers; i) a first plurality of refrigeration compressors connected to the first gas turbine; j) a second gas turbine in gaseous communication with the plurality of gas driers; k) a second plurality of refrigeration compressors connected to the second gas turbine; l) a mercury adsorber in gaseous communication with the plurality of gas driers; m) a filter in gaseous communication with the mercury adsorber; n) a plurality of coolers in gaseous communication with the filter; o) a scrub column in gaseous communication with the plurality of coolers; p) a cryogenic heat exchanger in gaseous communication with the scrub column; q) a LNG storage tank in fluid communication with the cryogenic heat exchanger; r) a boil off gas compressor in gaseous communication with the LNG storage tank; s) a high speed motor connected to the boil off gas compressor; t) a variable frequency drive connected to the high speed motor; and u) a waste heat recovery system, comprising: i) a first steam generator in gaseous communication with the first gas turbine; ii) a second steam generator in gaseous communication with the second gas turbine; iii) a steam turbine in gaseous communication with the first steam generator and the second steam generator; and iv) an electrical generator connected to the steam turbine. 